In order to evaluate whether the prophylactic use of fluoroquinolones diminishes the incidence of infections and/or mortality during neutropenia, we undertook a prospective, aleatory and controlled study in non-hospitalized adult patients with acute leukemia and chemotherapy-induced neutropenia including twenty five episodes of neutropenia including twenty five episodes of neutropenia which had occurred in 14 patients who were randomly selected either to receive or not quinolones (norfloxacin 800 mg daily or ciprofloxacin 1000 mg daily). Both groups were similar in terms of sex, age, underlying disease, chemotherapy for hematologic malignancy, duration and severity of neutropenia. The use of quinolones was associated with a delay in the fever onset during neutropenia (p = 0.0448), a decrease in the proportion of neutropenic febrile days (p = 0.0456), a decrease of infections caused by gram-negative bacilli (p = 0.037) and an increase of Streptococcus infections (p = 0.0857). There was no significant decrease in mortality, incidence of severe infections, proportion of neutropenic episodes without fever, empiric use of amphotericin B or fungal infections between both groups. The results of this study demonstrate that the prophylactic use of fluoroquinolones does not diminish the infectious morbidity and/or mortality in these patients.